Diversity of the inferior frontal gyrus-A meta-analysis of neuroimaging studies

Purpose: The inferior frontal gyrus (IFG) has attracted a lot of interest due to its involvement in motor control and language processing. More recently, it has also been implicated for the processing of empathy. The aim of this meta-analysis was to investigate if neuroimaging studies in humans reveal distinct foci related to empathy as compared to those in motor and speech control in the IFG. Materials and methods: We reviewed MEDLINE for functional imaging studies on healthy subjects published between 1991 and 2007. With the search terms inferior frontal gyms, and statistical parametric mapping 485 studies were identified. We performed a non-hierarchical cluster-centre analysis of the stereotactic coordinates of the reported 1042 significant activation peaks and investigated seven functional categories using a score of specificity (SCSP). Results: We found four significant, spatially distinct clusters. Three left-hemispheric clusters included one for processing of empathy, one closely adjacent for semantic and phonological processing, and one for working memory, while one cluster for fine movement control was located in the right hemisphere. Conclusions: This meta-analysis demonstrates a spatio-functional diversity of the left human IFG for processing of language, working memory and empathy. Notably, phonological and semantic processing collapsed into one cluster. Fine movement control located in a cluster in the right IFG occurred in a virtually mirror-like location to processing of empathy in the left hemisphere. These observations are in accordance with the notion of the mirror neuron system mediating specialized links between perception and action. (C) 2011 Elsevier B.V. All rights reserved.